Sleep mask



FIG. 1 is a perspective view of a sleep mask showing my new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is a top view thereof;

FIG. 7 is a bottom view thereof;

FIG. 8 is a second perspective view thereof; and,

FIG. 9 is a right side cross-section view thereof.

The broken lines in the drawings show environment that forms no part of the claimed design. 

CLAIM The ornamental design for a sleep mask, as shown and described. 